O

Aspergillus niger 2 days

MeO HO

FIGURE 15.169 Biotransformation of 6-shogaol (608) by Aspergillus niger.

6-Gingerol (613) (1 g) was treated in the same condition as mentioned above to yield six metabolites, wl-hydroxy-6-gingerol (614, 39.8%), its carboxylic derivative (616, 14.5%), a g-lactone (618) (16.9%) that might be formed from (616), its 8-hydoxy-g-lactone (619, 12.1%), w2-hydroxy-6-gin-gerol (615, 19.9%), and 6-deoxy-gingerol (617, 14.5%) (Takahashi et al., 1993).

The metabolic pathway of 6-gingerol (613) resembles that of 6-shagaol (608). That of 6-shogaol and dihydrocapsaicin (600) is also similar since both substrates gave carboxylic acids as the final metabolites (Takahashi et al., 1993) (Figure 15.170).

In conclusion, a number of sesquiterpenoids were biotransformed by various fungi and mammals to afford many metabolites, several of which showed antimicrobial and antifungal, antiobesity, cytotoxic, neurotrophic, and enzyme inhibitory activity. Microorganisms introduce oxygen atom at allylic position to give secondary hydroxyl and keto groups. Double bond is also oxidized to give epoxide, followed by hydrolysis to afford a diol. These reactions precede stereo- and regiospecifi-cally. Even at nonactivated carbon atom, oxidation reaction occurs to give primary alcohol. Some fungi like Aspergillus niger cleave the cyclopropane ring with a 1,1-dimethyl group. It is noteworthy that Aspergillus niger and Aspergillus cellulosae produce the totally different metabolites from the same substrates. Some fungi occurs reduction of carbonyl group, oxidation of aryl methyl group, phenyl coupling, and cyclization of a 10-membered ring sesquiterpenoids to give C6/C6- and C5/ C7-cyclic or spiro compounds. Cytochrome P-450 is responsible for the introduction of oxygen function into the substrates.

The present methods are very useful for the production of medicinal and agricultural drugs as well as fragrant components from commercially available cheap, natural, and unnatural terpenoids or a large amount of terpenoids from higher medicinal plants and spore-forming plants like liverworts and fungi.

The methodology discussed in this chapter is a very simple one-step reaction in water, nonhaz-ard, and very cheap, and it gives many valuable metabolites possessing different properties from those of the substrates.

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